1. Technical Field
The present invention relates to ceramic thermal barrier coatings, commonly referred to by the acronym, TBC, that is deposited and attached directly to a metallic substrate, or upon an intermediate bond coating deposited on, an covering such a substrate.
The invention also relates to a method of applying a TBC on a substrate, the TBC being applied on the substrate or a intermediate bond coating between the substrate and the TBC, preferably by means of thermal spraying of a powder that forms the TBC on the substrate or bond coating.
The invention also relates to metallic substrates and articles coated with such ceramic TBCS. In particular, the present invention concerns substrates and articles that constitute a constructional element operating in a high temperature environment, such as a turbine blade or combustor in a gas turbine engine.
2. Background
The demand for increased operating temperature in gas turbine engines has led to the development of ceramic thermal barrier coatings (TBC) constituted by materials that are deposited onto metallic parts such as turbine blades and that are exposed to high temperature environments. The task of the TBC is typically to thermally insulate metallic part(s) in order to prolong the parts” service life and prevent rapid degeneration due to temperature-severe operative conditions.
Normally an intermediate bond coating such as a MCrAlY-coating is applied to the metallic substrate in order to promote an efficient connection between the TBC and the metallic substrate. The TBC is applied to the bond coating by means of any suitable deposition technique such as thermal (preferably plasma) spraying, physical vapor deposition (PVD), or chemical vapor deposition (CVD).
Accordingly, the TBC should possess a thermal conductivity that is as low as possible and that presents sufficient thermo-mechanical properties such as thermal shock and cycling resistance, as well as be thin in order to save weight and space.